Have tried clearing cache, cookies, opened the firewall, added klaviyo to contacts, still no luck.

Shout up if you have any ideas? thanks Tim

For any other users that may encounter this in the future, the first steps we ask you to take which @chiatin has already explored (which is greatly appreciated) are the following:

1. Check your Junk/Spam folder
2. Please search for the words, “Confirm your Klaviyo email”
3. Check any filter or firewall settings as it may have been filtered
4. Add support@klaviyo.com to your contacts and please retry to send the message